Box shaped bilge keel

ABSTRACT

A box shaped bilge keel comprises a convex polygonal shaped cross-section. Further, the box shaped bilge keel extends along a pre-determined length of a hull of a floating vessel. Also, the box shaped bilge keel is providing additional width to the hull at the bottom of the floating vessel.

FIELD OF THE INVENTION

Embodiments of the present invention relate to floating vessels and more particularly to a box shaped bilge keel for the floating vessels.

BACKGROUND ART

Dynamic motions for floating vessels such as FSRUs (Floating Storage Regasification Units) are important design considerations during initial stages of design. Dynamic motions such as heave, roll and pitch motions introduce additional loads on hull structure and operational restrictions during the loading/offloading of cargo. Also, higher dynamic motions affect crew operability and comfort. Bilge keels are usually employed at sides of the floating vessels to reduce tendency of the floating vessels to roll.

Generally, bilge keels are in the form of a ‘strake’ or ‘plate’ on the sides of the floating vessels. Some of the bilge keel designs have been discussed below:

U.S. Pat. No. 6,176,191B1 discloses bilge keels for an FPSO type petroleum production system. The bilge keels have two lines of plates, one being continuous and another being sectioned. Further, the plates may be planar or corrugated.

JP2000219188A discloses discontinuous type bilge keels for a small watercraft. Further, since the bilge keels are discontinuous type, they are easy to maintain or replace.

U.S. Pat. No. 7,500,440B2 discloses a sponson and a wing keel arrangement for a floating vessel, instead of a traditional bilge keel. The sponson and the wing keel together provide stability to the floating vessel. Additionally, the wing keel may be pivotable, so as to act as a gate for a lower section of the sponson.

The aforesaid documents and other solutions may aim to provide bilge keels for floating vessels, however they still suffer from a number of deficiencies. First, most of the bilge keels are made of plates, while plates can provide only limited stability to the floating vessel. Further, the plates do not have any impact on reducing heave and pitch motions. Moreover, the sponson and the wing keel arrangement is rather complex and comparatively expensive to implement.

Therefore, there remains a need in the art for a bilge keel which does not suffer from above mentioned deficiencies.

Any discussion of the background art throughout the specification should in no way be considered as an admission that such background art is prior art nor that such background art is widely known or forms part of the common general knowledge in the field.

SUMMARY OF THE INVENTION

The present invention is described hereinafter by various embodiments. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein. Rather, the embodiment is provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art.

Embodiments of the present invention aim to provide a box shaped bilge keel of a floating vessel. The box shaped bilge keel comprises a convex polygonal shaped cross-section. A convex polygon is defined as a polygon with all its interior angles less than 180°. This means that all the vertices of the polygon will point outwards, away from the interior of the shape. Further, the box shaped bilge keel extends along a pre-determined length of a hull of the floating vessel.

In accordance with an embodiment of the present invention, the convex polygonal shaped cross-section is extending along the length of the hull, in a continuous manner.

In accordance with an embodiment of the present invention, the convex polygonal shaped cross-section is extending along the length of the hull, in form of a plurality of discontinuous segments.

In accordance with an embodiment of the present invention, the cross-section of the bilge keel is, but not limited to, square.

In accordance with an embodiment of the present invention, the box shaped bilge keel further comprises two tapered sections, one at each of a forward end and an aft end of the hull, respectively.

The box shaped bilge keel offers a number of advantages. The box shaped bilge keel generates more damping for roll and heave motions and reduces pitch motion considerably as compared to the traditional bilge keels.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may have been referred by examples, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical examples of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective examples.

These and other features, benefits, and advantages of the present invention will become apparent by reference to the following text figure, with like reference numbers referring to like structures across the views, wherein:

FIG. 1 illustrates a cross-sectional view of a bilge keel arrangement of a prior art;

FIG. 2 illustrates a plan view of the bilge keel arrangement of the prior art;

FIG. 3 illustrates a plot showing Response Amplitude Operators (RAO) of a roll amplitude of a floating vessel of the prior art;

FIG. 4 illustrates a mid-ship section view of an exemplary advanced floating vessel in accordance with an embodiment of the present invention;

FIG. 5 illustrates a plan view of the exemplary advanced floating vessel of FIG. 4, in accordance with an embodiment of the present invention; and

FIG. 6 illustrates a plan view of the exemplary advanced floating vessel of FIG. 4, in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Detailed embodiments of the present disclosure are described herein; however, it is to be understood that disclosed embodiments are merely exemplary of the present disclosure, which may be embodied in various alternative forms. Specific process details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present disclosure in any appropriate process.

The terms used herein are for the purpose of describing exemplary embodiments only and are not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” or “comprising,” when used in this specification, do not preclude the presence or addition of one or more components, steps, operations, and/or elements other than a mentioned component, step, operation, and/or element.

The embodiments of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, which form a part hereof, and which show, by way of illustration, specific example embodiments. The following detailed description is not intended to be taken in a limiting sense.

FIG. 1 illustrates a cross-sectional view of a bilge keel arrangement (100) of a prior art. As shown in FIG. 1, the bilge keel arrangement (100) comprises a bilge keel (140) provided at a side shell (110) of a floating vessel. The side shell (110) is defined between a molded line of bottom shell (130) and a molded line of side shell (120). FIG. 2 illustrates a plan view (200) of the bilge keel arrangement (100) of the prior art. As shown in FIG. 2, the bilge keel arrangement (100) comprises a bilge keel (140) and a base plate (210). The base plate (210) is attached to the side shell (110) and the bilge keel (140) is attached to the base plate (210) by means of welding. As can be seen from the FIGS. 1 and 2, the bilge keel (140) is in form of a plate.

FIG. 3 illustrates a plot showing Response Amplitude Operators (RAO) of a roll amplitude of the floating vessel. Response Amplitude Operators (RAO) are first order motion of a response of the floating vessel to regular waves of given period and amplitude. In the dynamic analysis, the floating vessel moves harmonically, in all 6 degrees of freedom, about its primary position. These harmonic motions are estimated by calculating the RAO amplitudes and phases, for all degrees of freedom and usually for a range of wave periods and directions. FIG. 3 illustrates typical RAOs of a roll amplitude with and without the bilge keel (140).

FIG. 4 illustrates a mid-ship section view of an exemplary advanced floating vessel in accordance with an embodiment (400) of the present invention. The exemplary advanced floating vessel has a box shaped bilge keel (420). The floating vessel may be, but not limited to, a ship, a boat or any other watercraft. In various embodiments, the floating vessel may be a floating Storage Regasification Unit (FSRU). The FSRU is the vital component required while transiting and transferring Liquefied Natural Gas (LNG) through the oceanic channels. Thus, FSRU is termed as a special type of ship which is used for LNG transfer.

FSRUs provide a useful solution for problems faced during transportation of LNG. A slight mistake may result in loss of precious lives and equally precious fuel, not to mention further degradation of the oceanic eco-system. The LNG fuel is semi-cooled and transported in a slushy state of −160° at the required destination. But the fuel needs to be heated up to its original gaseous state before the gas is pumped into its storage systems. The whole process of freezing and then re-heating the fuel is extremely expensive not to mention time-consuming. Therefore, FSRUs provide a viable solution. The FSRUs may be equipped as a separate unit aboard the LNG carrier itself or an old gas carrier can be converted into an independent FSRU and placed in a particular destination. The FSRU is capable of carrying out the process of freezing and reheating within the vessel itself without having to unload the fuel in its semi-frozen slushy state.

Further, the main components of FSRUs are LNG transfer system (offloading system), storage tanks, (in ship), Boil-off gas (BOG) handling system, LNG pumping system, vaporization equipment, delivery facility, and auxiliary systems. In the FSRU, the LNG delivered by LNG carriers is received by the FSRU offloading system and stored in tanks. Then, LNG is pumped and re-gasified into natural gas and delivered to consumers through a flexible or rigid riser, connected to the subsea pipeline or via high-pressure loading arms fixed on a jetty. Prior to its delivery, the natural gas flow rate is measured by an ultrasonic flow meter and the gas is odorized.

As can be seen from the FIG. 4, the box shaped bilge keel (420) comprises a substantially convex polygonal shaped cross-section, extending along a substantial length of a hull (410). The hull is the watertight body of a ship or boat. The structure of the hull varies depending on the vessel type. In a typical modern steel ship, the structure consists of watertight and non-watertight decks, major transverse and watertight (and also sometimes non-tight or longitudinal) members called bulkheads, intermediate members such as girders, stringers and webs and minor members called ordinary transverse or longitudinal frames, depending on the structural arrangement.

A convex polygon is defined as a polygon with all its interior angles less than 180°. This means that all the vertices of the polygon will point outwards, away from the interior of the shape. In accordance with an embodiment, the substantially convex polygonal shaped cross-section is extending along the substantial length of the hull (410) continuously. In accordance with another embodiment, the substantially convex polygonal shaped cross-section is extending along the substantial length of the hull (410) in form of a plurality of discontinuous segments. In accordance with an embodiment, the cross-section of the bilge keel (420) is, but not limited to, substantially square, rectangle, rhombus, or pentagon. In accordance with an embodiment, the hull (410) is a box shaped hull, and the box shaped bilge keel (420) has been provided at a bottom of the hull (410). The box shaped hull (410), also called as a two chine hull, has a flat bottom and nearly vertical sides. This design provides far more stability than a ‘V’-shaped single chine hull, with minimum draft and a large cargo capacity. These characteristics make the two chine hull popular for punts, barges and scows. In accordance with an embodiment, the length of the box shaped bilge keel (420) is around 80% of the length of the hull (410).

FIG. 5 illustrates a plan view of the exemplary advanced floating vessel of FIG. 4, in accordance with an embodiment (500) of the present invention. As shown in FIG. 5, the box shaped bilge keel (420) comprises two tapered sections (4202 and 4204), one at each of a forward end (510) and an aft end (520) of the hull (410), respectively. Also, the substantially convex polygonal shaped cross-section is extending along the substantial length of the hull (410) continuously. FIG. 6 illustrates a plan view of the exemplary advanced floating vessel of FIG. 4, in accordance with another embodiment (600) of the present invention. As shown in FIG. 6, the substantially convex polygonal shaped cross-section is extending along the substantial length of the hull (410) in form of a plurality of discontinuous segments (610).

The box shaped bilge keel (420) provides additional width to the hull (410) at the bottom generating higher damping for roll, pitch and heave motions compared to the bilge keel (140) of the prior art. The box shaped bilge keel (420) reduces the peaks in RAO curves around the natural period of the floating vessel considerably.

The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. Examples and limitations disclosed herein are intended to be not limiting in any manner, and modifications may be made without departing from the spirit of the present disclosure. Those skilled in the art will recognize that many variations are possible within the spirit and scope of the disclosure, and their equivalents, in which all terms are to be understood in their broadest possible sense unless otherwise indicated.

Various modifications to these embodiments are apparent to those skilled in the art from the description and the accompanying drawings. The principles associated with the various embodiments described herein may be applied to other embodiments. Therefore, the description is not intended to be limited to the embodiments shown along with the accompanying drawings but is to be providing broadest scope of consistent with the principles and the novel and inventive features disclosed or suggested herein. Accordingly, the disclosure is anticipated to hold on to all other such alternatives, modifications, and variations that fall within the scope of the present disclosure and appended claims. 

1. A box shaped bilge keel of a floating vessel, the box shaped bilge keel comprising a convex polygonal shaped cross-section, wherein the box shaped bilge keel extends along a pre-determined length of a hull of the floating vessel.
 2. The box shaped bilge keel as claimed in claim 1, wherein the convex polygonal shaped cross-section is extending along the length of the hull, in a continuous manner.
 3. The box shaped bilge keel as claimed in claim 1, wherein the convex polygonal shaped cross-section is extending along the length of the hull, in form of a plurality of discontinuous segments.
 4. The box shaped bilge keel as claimed in claim 1, wherein the cross-section of the bilge keel is square.
 5. The box shaped bilge keel as claimed in claim 1, further comprising two tapered sections, one at each of a forward end and an aft end of the hull, respectively. 